The Catholic Church is the oldest institution in the western world, and with more than one billion members worldwide, it is the largest Christian church. Its history spans almost 2,000 years and is rooted in the Church's Canon of Scripture and Tradition. At the head of the church is the Pope, who Catholics believe is the successor to Saint Peter whom Christ appointed as the first head of His church. The Pope, according to the religion's doctrine, can speak infallibly on matters of faith and morals. The Catholic Church practises closed communion and only baptised members of the church are permitted to receive the Eucharist, or Holy Communion.

Pope Francis flew in to a papal residence near Rome yesterday for an unprecedented encounter with "pope emeritus" Benedict - the first time a pontiff has met his predecessor.

The talks in the town of Castel Gandolfo round off a historic few weeks for the Roman Catholic Church after Benedict became the first pope to resign in 600 years and only the second to do so by choice in 2,000 years.

The last pope to resign - Celestine V in 1294 - was locked up and perhaps killed off by his successor, Boniface VIII, and there is no record of the two ever meeting post-resignation.

The two men dressed in white embraced warmly on the helipad in the gardens of Castel Gandolfo, where Benedict has been living since he stepped down February 28 and became the first pope to resign in 600 years.

In a series of gestures that ensued, Benedict made clear that he considered Francis to be pope while Francis made clear he considered his predecessor to be very much a revered brother and equal. They clasped hands repeatedly, showing one another the deference owed a pope in ways that surely turned Vatican protocol upside down.

Travelling from the helipad to the palazzo, Francis sat on the right-hand side of the car, the traditional place of the pope, while Benedict sat on the left. When they entered the chapel inside the palazzo to pray, Benedict tried to direct Francis to the papal kneeler at the front of the chapel, but Francis refused.

"No, we are brothers," Francis told Benedict, according to the Vatican spokesman the Reverand Federico Lombardi. He said Francis wanted to pray together with Benedict, so the two used a different kneeler in the pews and prayed side-by-side.

Francis also brought a gift to Benedict, an icon of the Madonna, and told him that it's known as the "Madonna of Humility".

"I thought of you," Francis told Benedict. "You gave us so many signs of humility and gentleness in your pontificate."

Benedict replied: "Grazie, grazie."

Walking with a cane, the 85-year-old Benedict looked frail compared to the robust 76-year-old Argentine.

Outside the villa, the main piazza of Castel Gandolfo was packed with well-wishers bearing photos of both popes and chanting "Francesco! Francesco!"

The Vatican downplayed the remarkable reunion in keeping with Benedict's desire to remain "hidden from the world" and not interfere with his successor's papacy.

There was no live coverage by Vatican television, and only a short video and still photos were released after the fact.

The Vatican spokesman said the two spoke privately for 40-45 minutes, followed by lunch with the two papal secretaries, but no details were released.

The secrecy has led to enormous speculation about what these two men in white might have to say to one another.

The two leaders of the world's 1.2 billion Catholics are both preoccupied with issues ranging from rising secularism in Western countries to the reform of Vatican bureaucracy to the ongoing scandal over the sexual abuse of children by clerics.

Some Church scholars worry that in the event that Francis undoes some of Benedict's policies while he is still alive, the former pope could become a lightning rod for conservatives and polarise the Church.

Additional reporting by Reuters, Agence France-Presse

This article appeared in the South China Morning Post print edition as Pope visits Benedict at Italian retreat